1. Field of the Invention
The present invention relates to differential pressure flow measurement and more particularly to differential pressure transducers capable of transducing such differential pressure into an electric signal. It is a general practice to measure process flow by inserting a restrictive means, such as an orifice, in the process pipe line to obtain a pressure difference before and after the restrictive means. This differential pressure corresponds to the flow of the fluid passing through the pipe line. This differential pressure may be utilized in a differential pressure transducer to cause a displacement of means, such as a diaphragm, and such displacement can be detected by electrical devices and converted into measurable electrical signals propotional to the displacement and hence to pressure differential and fluid flow.
2. Description of the Prior Art
A prior art differential pressure transducer is disclosed in U.S. Pat. Nos. 3,238,479 and 3,336,525. The general construction of such a transducer is illustrated, as an aid to better understanding of the present invention, in sectional view in FIG. 1. Referring to FIG. 1, there is seen a diaphragm 2 located in the center cavity of a case 1. The pressure of the fluid being measured is led into two chambers 31 and 32 which are separated by the diaphragm 2. A pressure difference developed between the two chambers displaces the diaphragm 2. This displacement is detected by detection coils 41 and 42 on the principle of eddy current production. The case 1, the diaphragm 2, and the cores 51 and 52 of the detection coils of such a transducer are made of non-magnetic material, and the transducer is simple in construction.
However, such prior art transducers have drawbacks. For example, electrical energy may leak from the detection coils since these coils are in direct contact with the fluid being measured. This undesirably decreases the safety sought in pressure-resistant and explosion-proof instruments. Furthermore, if an excess pressure is led into the transducer, the diaphragm 2 is likely to be subject to excessive deformation and a permanent strain may be introduced into the diaphragm. Moreover, if it is desired to detect the differential pressure with high accuracy, specific steps must be taken such as, for example, increasing the frequency of AC power supplied to the detection coils, because the case 1, the diaphragm 2, and the cores 51 and 52 are made of non-magnetic material. Thus, such prior art transducer possesses practical limitations for flow measurements in the process industry.